The present invention relates to a semiconductor module provided with a built-in antenna element and more particularly, a semiconductor module for radio communications or distance measurements which has a built-in antenna element suited for a radio communications system or a distance/speed measurements system using a millimeter-wave band ranging from 30 GHz to 300 GHz and a quasi-millimeter -wave band ranging from 18 GHz to 30 GHz, for example.
As known, a radio communications system of heterodyne type substantially comprises a mixer circuit, frequency converter circuit including local oscillators, an amplifier circuit, and an antenna element, for example.
In a conventional radio communications system using frequencies lower than quasi-millimeter-waves, a plurality of devices, each having the above components, except the antenna element, sealed in a package or casing, are connected to each other by external terminals mounted to the casings of the devices thus constituting a subsystem for radio communications.
A technique is also known that a combination of the frequency converter circuit and the amplifier circuit which is embodied as a microwave integrated circuit is mounted together with the antenna element in a wave-guide which is a microwave circuit for transmission of a microwave through the waveguide (for example, as disclosed in Jpn. Pat. Appln. KOKOKU Publication No. 56-17842 or No. 57-44241).
A phased array antenna is known in which a plurality of transmitter and receiver antennas are arranged two-dimensionally.
In common, such a phased array antenna includes cables and connectors for power supply from a microwave integrated circuit to an antenna element.
Accordingly, the above mentioned prior art systems will be troublesome in carrying out a maintenance work even worse, the signal processing ability of such prior art systems may decline due to joint degradation or deterioration with time of the cables and connectors.
The prior art systems also have disadvantages in that there is interference between the antenna element and the microwave circuit and in that the distance between the antenna elements in a two-dimensional arrangement is not small.
The former disadvantage which is inevitable in the power supply from the microwave circuit to the antenna element, may be eliminated by means of a construction which is depicted in Jpn. Pat. Appln. KOKAI Publication No. 63-316905 as shown in FIGS. 9A and 9B.
FIGS. 9A and 9B are identical to FIGS. 1 and 2 of the prior art disclosed in the Publication No. 63-316905.
As shown in FIGS. 9A and 9B, one of antenna elements which constitute a phased array antenna is connected to a microwave circuit.
Referring to FIG. 9A, the antenna element is denoted by 21 while a package is denoted by 22.
The package 22 contains the microwave integrated circuit 23.
Referring to FIG. 9B which is an enlargement of FIG. 9A, the microwave integrated circuit 23 consisting mainly of a microwave IC chip 23a is welded by a dose of solder 22b to the package 22.
The microwave integrated circuit 23 also has a via-hole 23c as the main passage and via-holes 23d for grounding a back electrode 23e in the shortest distance.
More specifically, a transmitter/receiver terminal 23f of the microwave integrated circuit 23 is electrically connected through the via-hole 23c of the main passage to the antenna element 21.
This arrangement can eliminate the former disadvantage derived from the cables and connectors between the antenna element and the transmitter/receiver module.
For solving the disadvantages relating to interference between the antenna element and the microwave circuit and the small distance between the antenna elements in a two-dimensional arrangement, a method is known as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 6-77729.
FIGS. 10A and 10B are identical to FIGS. 1(a) and 1(b) of the prior art depicted in the Jpn. Pat. Appln. KOKAI Publication No. 6-77729.
Shown in FIGS. 10A and 10B similar to FIGS. 9A and 9B are one of antenna elements which constitute a phased array antenna and a microwave circuit joined integrally with the antenna.
FIG. 10A is a perspective view and FIG. 10B is a cross sectional view taken along the line XB--XB of FIG. 10A.
As shown in FIGS. 10A and 10B, the antenna element denoted by numeral 33 is mounted on a dielectric substrate 31 having a ground 32 provided on the back side thereof and a semiconductor circuit board 34 including a microwave circuit composed using portions of the dielectric substrate 31 and the ground 32.
The antenna element 33 is coupled to the microwave circuit via a coupling aperture 35 provided in the ground 32.
The construction shown in FIGS. 10A and 10B like that shown in FIGS. 9A and 9B allows the microwave circuit and the antenna element to be located on the front and back sides of the dielectric substrate 31 respectively.
Since the microwave circuit and the antenna element shown in FIGS. 10A and 10B are disposed on the front and back sides of the dielectric substrate 31 respectively at corresponding locations to form a phased array antenna, the disadvantage that the distance between any two adjacent antenna elements in a two-dimensional arrangement is not small will be eliminated.
In addition, the microwave circuit is located directly on the ground over the back side of the dielectric substrate as shown in FIGS. 10A and 10B and is spaced from the antenna element so that interference between the microwave circuit and the antenna element can be prevented.
An ultra-high frequency band radio communications apparatus is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 9-153839 in which a transmitter antenna, a receiver antenna, and a semiconductor chip are mounted in a single package. The transmitter antenna, the receiver antenna, and the semiconductor chip are located on a substrate which is a planer substrate having a single mounting surface. The space where the transmitter and receiver antennas are disposed is communicated with a space of which cut-off frequency is high enough to reject the carrier frequency of the radio communications apparatus. The semiconductor chip is located in an intermediate between the two spaces. The package is covered at top with a non-conductive cap. The intermediate between the two spaces is protected with a layer of a conductive material. The ultra-high frequency band radio communications apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 9-153839 is advantageous in decreasing the overall dimensions as well as reducing the cost of production, compared with the conventional communication systems using the wave-guide techniques.
As a great number of commercial radio apparatuses have widely been marketed, it has been desired to develop and design the lowest cost and most minimized design radio communications systems which may play a major role in the field of large data transmission.
Particularly, personal systems such as namely desk-top personal computers prevail today and some of them are connected to each other for mutual use of data in a network such as LAN.
In such a network, the exchange of data between the personal systems is preferably implemented by means of radio communications in view of the advantage of mobility and the versatility of location of the systems.
It is thus essential for such radio communications systems to be easy in handling and free of the location and method of installation.
In this point of view, the conventional technique in which the devices having the electronic components, except the antenna element, sealed in a casing are utilized in a combination is hardly applicable to the development of millimeter-wave radio communications systems.
If the conventional technique is embodied in a millimeter-wave radio communications system, parasitic factors pertinent to an individual sealed casing are emphasized through higher frequency waves and may be uncontrollable parameters.
In a communications subsystem or radio communications system in which the devices which have the components, except the antenna element, sealed in a single casing are utilized in a combination, the uncontrollable parameters derived from the parasitic factors cause the system performance to hardly reach its desired level.
The constructions disclosed in the Jpn. Pat. Appln. KOKOKU Publication No. 56-17842 or No. 57-44241 is substantially provided with a microwave circuit such as a waveguide and will be unfavorable in the installation in a radio communications system as well as in the mobility and the cost-saving of the same.
It is hence desired that the components including the antenna element are hermetically sealed for maintaining a durability and reliability so that they can be used as a most preferable device in a radio communication system which is thus facilitated in handling and not limited in the location and method of installation.
However, since an electromagnetic wave is radiated from the antenna element, the size of the window through which the electromagnetic wave can transmit is at least three times greater than the size of the antenna element.
In the foregoing prior art, a microwave is used for transmission of signals. When the frequency of the a microwave is 10 GHz, the size of the antenna element is possibly 3 cm.
Accordingly, the size of the electrical wave radiating window is 9 cm hence increasing the overall dimensions of the sealed device of the antenna element provided integrally with the microwave circuit and thus the radio communications system.
With the prior art construction, it is very difficult to provide an antenna element sealed device which is easy in handling and free of the location and method of installation.
According to the prior art devices disclosed in the Jpn. Pat. Appln. KOKAI Publication No. 63-316905 or No. 6-77729, the microwave circuit and the antenna element are mounted on the front and back sides of the substrate respectively in opposite relationship.
In general, the microwave circuit is patterned on a GaAs semiconductor substrate and the antenna element is provided on a dielectric substrate such as ceramic.
For fabricating the prior art device, the two substrates are pasted up to each other so that the microwave circuit is located opposite to the antenna element. This is a troublesome task and will increase the cost of production.
Also, there is developed a problem of thermal dissipation.
The ceramic substrate on which the antenna element is placed is lower by ten times or more in the thermal conductivity than copper or tungsten material and unfavorable to assist radiation of heat from the microwave circuit in the semiconductor device.
In the prior art device disclosed in the Jpn. Pat. Appln. Publication KOKAI No. 9-153839, a semiconductor chip is mounted on the substrate carrying the transmitter and receiver antenna elements. Since the antenna element is provided in a pattern on a dielectric, the substrate has to be made of a dielectric material. The thermal conductivity of a dielectric material is however lower than that of any metal. For example, the thermal conductivity of copper is 381 W/m k while alumina is as low as 21 W/m k.
Also, it is said the package is accompanied with the cap. The semiconductor chip to be mounted is unpackaged, i.e. a bare semiconductor chip. In common, a semiconductor chip has to be hermetically sealed for preventing oxygen and water deterioration to maintain reliability. The hermetical sealing can be adjusted by resistance welding of koval to the leak rate ranging from 10.sup.-9 to 10.sup.-10 (cc/sec 1 atm) or with the use of plastic and araldyte to the leak rate ranging from 10.sup.-5 to 10.sup.-6 (cc/sec 1 atm), for example.
It is common for device experts to provide a semiconductor chip with hermetical sealing but not for radio specialists. For example, some ultra-high frequency band radio communications devices have bare semiconductor chips provided without hermetical sealing as depicted in "C-142 60-GHz band high/ultra high digital transmission receiver module", the Institute of Electronics, Information and Communication Engineers, Aug. 15, 1995, "Microwave semiconductor device", Jpn. Pat. Appln. KOKAI Publication No. 57-141944, "Low-noise amplifier", Jpn. Pat. Appln. KOKAI Publication No. 61-48201, and "A W-band monolithic low noise AlGaAs/InGaAs pseudomorphic HEMT amplifier mounted on a small hermetically sealed package with waveguide interface", 1995 IEEE MTT-S Digest, PP. 207-210.